Aromatic hydrocarbons, such as benzene, toluene, xylene, etc., are useful as fuels, solvents, and as feeds for various chemical processes. Of the xylenes, para-xylene (“p-xylene”) is particularly useful for manufacturing phthalic acids such as terephthalic acid, which is an intermediate in the manufacture of synthetic fibers, such as polyester fibers.
Xylenes can be produced from naphtha by processes such as steam cracking. Besides p-xylene, the C8 aromatic portion of a steam cracker effluent generally contains significant amounts of orthoxylene, metaxylene, and ethylbenzene. These molecules all have similar boiling points, which lead to difficulties in separating the p-xylene for conversion to terephthalic acid. Conventional methods for separating C8 aromatics generally utilize complex, high-cost, energy-intensive separations process, e.g., those utilizing superfractionation and/or multistage refrigeration steps.
It is desirable to produce terephthalic acid from hydrocarbon with fewer/less stringent separations.